Magnetic recording media comprising a non-magnetic support having provided thereon a magnetic layer containing ferromagnetic particles and a binder are now widely used for magnetic recording and reproducing.
When the above-described magnetic recording media are used, for example, as a video tape, dropouts generally occur. The reason is believed to be due to wear and scratches of a magnetic layer occurring from inside of the magnetic recording medium itself and due to attachment of, for example, dust and contaminants on the magnetic layer occurring from the outside of the magnetic recording medium.
As means to solve the former problem, running stability of a tape is increased by adding abrasive agents into a magnetic layer or film strength of a magnetic layer is increased by raising the glass transition temperature Tg of the binder of the magnetic layer, as described in U.S. Pat. Nos. 3,630,910 and 3,833,412.
On the other hand, as means to solve the latter problem, surface electrical resistance Rs of the magnetic recording medium is decreased by adding carbon black and electroconductive polymer into the magnetic layer, as described, for example, in Japanese Patent Publication No. 28648/72 and U.S. Pat. No. 4,539,257, since the latter problem is believed to be caused by the charging of the magnetic recording medium, that is, a tape is charged as a result of friction between layers of the tape or between the tape and foreign substances, and the resulting static charging induces dust and contaminants floating in the air.
However, the above means to prevent wear of a magnetic recording medium is not fully sufficient. Dropouts caused by scratches generated upon running a tape still occur. As means to prevent dust and contaminants from attaching on the magnetic recording medium, electroconductive substances such as carbon black are added to a magnetic layer to increase electroconductivity of the magnetic recording medium (or to decrease surface electric resistance) and to let the charged electric charge go. However, such means to prevent static electrical charging is also not fully sufficient. There is also an additional problem. That is, when a filler such as carbon black which is used to increase electroconductivity is used in a large amount, not only does runnability of a tape deteriorate, but the packing density of ferromagnetic particles also decreases, with the result that recording and reproducing characteristics become poor. When an abrasive agent is added to a magnetic layer to increase running stability, the same problem as above also occurs.